feat(invite-system): implement user invite functionality with registration mode control

server/config/mailer.js

@@ -139,3 +139,46 @@ export async function sendFederationInviteEmail(to, name, fromUser, roomName, me
     text: `Hey ${name},\n\nYou have received a meeting invitation from ${fromUser}.\nRoom: ${roomName}${message ? `\nMessage: "${message}"` : ''}\n\nView invitation: ${inboxUrl}\n\n– ${appName}`,
   });
 }
+
+/**
+ * Send a user registration invite email.
+ * @param {string} to          – recipient email
+ * @param {string} inviteUrl   – full invite registration URL
+ * @param {string} appName     – branding app name (default "Redlight")
+ */
+export async function sendInviteEmail(to, inviteUrl, appName = 'Redlight') {
+  if (!transporter) {
+    throw new Error('SMTP not configured');
+  }
+
+  const from = process.env.SMTP_FROM || process.env.SMTP_USER;
+  const headerAppName = sanitizeHeaderValue(appName);
+  const safeAppName = escapeHtml(appName);
+
+  await transporter.sendMail({
+    from: `"${headerAppName}" <${from}>`,
+    to,
+    subject: `${headerAppName} – You've been invited`,
+    html: `
+      <div style="font-family:Arial,sans-serif;max-width:520px;margin:0 auto;padding:32px;background:#1e1e2e;color:#cdd6f4;border-radius:12px;">
+        <h2 style="color:#cba6f7;margin-top:0;">You've been invited! 🎉</h2>
+        <p>You have been invited to create an account on <strong style="color:#cdd6f4;">${safeAppName}</strong>.</p>
+        <p>Click the button below to register:</p>
+        <p style="text-align:center;margin:28px 0;">
+          <a href="${inviteUrl}"
+             style="display:inline-block;background:#cba6f7;color:#1e1e2e;padding:12px 32px;border-radius:8px;text-decoration:none;font-weight:bold;">
+            Create Account
+          </a>
+        </p>
+        <p style="font-size:13px;color:#7f849c;">
+          Or copy this link in your browser:<br/>
+          <a href="${inviteUrl}" style="color:#89b4fa;word-break:break-all;">${escapeHtml(inviteUrl)}</a>
+        </p>
+        <p style="font-size:13px;color:#7f849c;">This link is valid for 7 days.</p>
+        <hr style="border:none;border-top:1px solid #313244;margin:24px 0;"/>
+        <p style="font-size:12px;color:#585b70;">If you didn't expect this invitation, you can safely ignore this email.</p>
+      </div>
+    `,
+    text: `You've been invited to create an account on ${appName}.\n\nRegister here: ${inviteUrl}\n\nThis link is valid for 7 days.\n\n– ${appName}`,
+  });
+}